The recent rapid directivity to digitization has led to increased opportunities of subjecting silver halide photographic materials to digital exposure. Along with such a trend, photographic color paper as a photographic material for color prints is desired with respect to suitability for exposure at a relatively high intensity for an extremely short time at the level of milli-seconds to nano-seconds and aptitude for scanning exposure.
There have been employed silver chloride emulsions or high chloride silver halide emulsions in color paper to achieve rapid processability. Further, it is commonly known that doping iridium compounds is effective to improve reciprocity law failure characteristics as a matter of properties of silver halide emulsions. There are disclosed high chloride silver halide emulsion grains having a high bromide region in the vicinity of the corners of the grains, as described in JP-A No. 64-26837 (hereinafter, the term JP-A refers to Japanese Patent Application Publication); high chloride silver halide emulsion grains in which a bromide-localized region is selectively doped with an iridium compound, thereby leading to superior latent image stability and reciprocity law failure characteristics, as described in JP-A No. 1-105940. There is also disclosed a method of forming a bromide-localized region by using silver bromide fine-grains doped with an iridium compound, as described in U.S. Pat. No. 5,627,020. However, neither of the foregoing methods was sufficient for improving latent image stability in the initial stage after exposure.
In digital exposure systems of the recent subject, it was proved that sufficient practical qualities were not achieved by only known techniques for improving latent image stability, in exposure suitability at a high intensity for an extremely short time. Techniques adaptable to such a digital exposure system include, for examples, chemical sensitization and spectral sensitization suitable for formation of a bromide-localized phase, as described in U.S. Pat. No. 5,601,513; and the use of a silver iodochloride emulsion, as described in European Patent Nos. 750,222 and 772,079.
However, it was proved in studies by the inventors of this application that the foregoing techniques for improving aptitude for digital exposure was not only insufficient for improving latent image stability but also resulted in marked deteriorated pressure resistance and pre-exposure storage stability of photographic materials. It is desired to immediately solve this matter.
JP-A No. 2001-188311 discloses a method for improving reciprocity law failure and coating composition stability, in which silver halide grains contain a bromide-rich or iodide-rich phase in the vicinity of the grain surface and introduction of such a rich phase is separated into two occasions, before and after addition of mercapto compounds. However, it was proved that using only this method was insufficient for improving storage stability of silver halide emulsions.
JP-A Nos. 6-19024 and 6-19026 disclose that adding non-labile di-chalcogen compounds before or during formation of silver halide grains, or during spectral/chemical sensitization of a silver halide emulsion improves fresh fog or aging fog. Further, JP-A No. 6-19037 discloses adding such compounds in the form of a solid particle dispersion and JP-A No. 6-35147 discloses that a silver chloride emulsion containing a diaminodisulfide compound and a sulfonate compound at a weight ratio of 1:1 to 1:20 improves storage stability and performance variation caused by temperature fluctuation at the time of exposure on color photographic materials.
JP-A No. 6-202265 discloses that adding a specific disulfide compound and a specific sulfinate or seleninate compound before or during spectral/chemical sensitization results in reduced fogging and enhanced sensitivity. There is also disclosed a photographic element comprising a silver chloride emulsion including a water-soluble disulfide compound, leading to reduced fogging, reduced variation in fog density and sensitivity after pre-exposure storage and reduced variation in sensitivity due to temperature fluctuation at the time of exposure, as described in JP-A No. 7-72580.
However, neither of the foregoing methods was sufficient in description and effectiveness with respect to latent image stability, storage stability and pressure resistance, specifically, latent image stability, storage stability and pressure resistance of emulsions exposed at a high intensity.
Though JP-A No. 6-148783, 6-175263 and so on discloses a photographic material containing a crown ether compound, there is scarce disclosure on detail of chemical sensitization, or spectral sensitization and therefore there is no teaching as for application to selenium sensitization.
A photographic element containing silver chloride grains having selenium compound at the surface of the grains (for example, Patent Document 1 and 2), it is not clear there is an improvement of photographic characteristics other than sensitivity. Particularly there is no disclosure on halide content or dopant which are necessary for improvement of characteristics such as gradation, latent image and so on. Therefore it is difficult to provide a practical silver halide photographic light sensitive material satisfying various characteristics demanded recently. There is a disclosure concerning silver halide photographic light sensitive materials in which selenium sensitization or tellurium sensitization is applied to silver chloride or silver chlorobromide grains having high chloride content (for example, Patent Documents 3, 4 and 5). However improvement effects on characteristics such as latent image stability or coating composition storage stability is not clear, and further the improvement of sensitivity and gradation recently demanded for silver halide photographic light sensitive materials is not satisfactory.
(Patent Document 1)
JP-A No. 5-66513
(Patent Document 2)
U.S. Pat. No. 5,240,827
(Patent Document 3)
JP-A No. 5-313293
(Patent Document 4)
JP-A No. 9-5922
(Patent Document 5)
JP-A No. 9-5924